The present invention relates to Alzheimer""s Disease, amyloid protein precursor, amyloid beta peptide, and human aspartyl proteases, as well as a method for the identification of agents that modulate the activity of these polypeptides and thereby are candidates to modulate the progression of Alzheimer""s disease.
Alzheimer""s disease (AD) causes progressive dementia with consequent formation of amyloid plaques, neurofibrillary tangles, gliosis and neuronal loss. The disease occurs in both genetic and sporadic forms whose clinical course and pathological features are quite similar. Three genes have been discovered to date which, when mutated, cause an autosomal dominant form of Alzheimer""s disease. These encode the amyloid protein precursor (APP) and two related proteins, presenilin-1 (PS1) and presenilin-2 (PS2), which, as their names suggest, are structurally and functionally related. Mutations in any of the three proteins have been observed to enhance proteolytic processing of APP via an intracellular pathway that produces amyloid beta peptide (Axcex2 peptide, or sometimes here as Abeta), a 40-42 amino acid long peptide that is the primary component of amyloid plaque in AD.
Dysregulation of intracellular pathways for proteolytic processing may be central to the pathophysiology of AD. In the case of plaque formation, mutations in APP, PS1 or PS2 consistently alter the proteolytic processing of APP so as to enhance formation of Axcex2 1-42, a form of the Axcex2 peptide which seems to be particularly amyloidogenic, and thus very important in AD. Different forms of APP range in size from 695-770 amino acids, localize to the cell surface, and have a single C-terminal transmembrane domain. Examples of specific isotypes of APP which are currently known to exist in humans are the 695-amino acid polypeptide described by Kang et. al. (1987), Nature 325: 733-736 which is designated as the xe2x80x9cnormalxe2x80x9d APP; the 751 amino acid polypeptide described by Ponte et al. (1988), Nature 331: 525-527 (1988) and Tanzi et al. (1988), Nature 331: 528-530; and the 770 amino acid polypeptide described by Kitaguchi et. al. (1988), Nature 331: 530-532. The Abeta peptide is derived from a region of APP adjacent to and containing a portion of the transmembrane domain. Normally, processing of APP at the xcex1-secretase site cleaves the midregion of the Axcex2 sequence adjacent to the membrane and releases the soluble, extracellular domain of APP from the cell surface. This xcex1-secretase APP processing creates soluble APP-xcex1, which is normal and not thought to contribute to AD. Pathological processing of APP at the xcex2- and xcex3-secretase sites, which are located N-terminal and C-terminal to the xcex1-secretase site, respectively, produces a very different result than processing at the a site. Sequential processing at the xcex2- and xcex3-secretase sites releases the Axcex2 peptide, a peptide possibly very important in AD pathogenesis. Processing at the xcex2- and xcex3-secretase sites can occur in both the endoplasmic reticulum (in neurons) and in the endosomal/lysosomal pathway after reinternalization of cell surface APP (in all cells). Despite intense efforts, for 10 years or more, to identify the enzymes responsible for processing APP at the xcex2 and xcex3 sites, to produce the Axcex2 peptide, those proteases remained unknown until this disclosure.
Here, for the first time, we report the identification and characterization of the xcex2 secretase enzyme, termed Aspartyl Protease 2 (Asp2). We disclose some known and some novel human aspartic proteases that can act as xcex2-secretase proteases and, for the first time, we explain the role these proteases have in AD. We describe regions in the proteases critical for their unique function and for the first time characterize their substrate. This is the first description of expressed isolated purified active protein of this type, assays that use the protein, in addition to the identification and creation of useful cell lines and inhibitors.
Here we disclose a number of variants of the Asp2 gene and peptide.
In one aspect, the invention provides any isolated or purified nucleic acid polynucleotide that codes for a protease capable of cleaving the beta (xcex2) secretase cleavage site of APP that contains two or more sets of special nucleic acids, where the special nucleic acids are separated by nucleic acids that code for about 100 to 300 amino acid positions, where the amino acids in those positions may be any amino acids, where the first set of special nucleic acids consists of the nucleic acids that code for the peptide DTG, where the first nucleic acid of the first special set of nucleic acids is the first special nucleic acid, and where the second set of nucleic acids code for either the peptide DSG or DTG, where the last nucleic acid of the second set of nucleic acids is the last special nucleic acid, with the proviso that the nucleic acids disclosed in SEQ ID NO. 1 and SEQ ID NO. 3 are not included. In a preferred embodiment, the two sets of special nucleic acids are separated by nucleic acids that code for about 125 to 222 amino acid positions, which may be any amino acids. In a highly preferred embodiment, the two sets of special nucleic acids are separated by nucleic acids that code for about 150 to 196, or 150-190, or 150 to 172 amino acid positions, which may be any amino acids. In a particular preferred embodiment, the two sets are separated by nucleic acids that code for about 172 amino acid positions, which may be any amino acids. An exemplary nucleic acid polynucleotide comprises the acid nucleotide sequence in SEQ ID NO. 5. In another particular preferred embodiment, the two sets are separated by nucleic acids that code for about 196 amino acids. An exemplary polynucleotide comprises the nucleotide sequence in SEQ ID NO. 5. In another particular embodiment, the two sets of nucleotides are separated by nucleic acids that code for about 190 amino acids. An exemplary polynucleotide comprises the nucleotide sequence in SEQ ID NO. 1. Preferably, the first nucleic acid of the first special set of amino acids, that is, the first special nucleic acid, is operably linked to any codon where the nucleic acids of that codon codes for any peptide comprising from 1 to 10,000 amino acid (positions). In one variation, the first special nucleic acid is operably linked to nucleic acid polymers that code for any peptide selected from the group consisting of: any reporter proteins or proteins which facilitate purification. For example, the first special nucleic acid is operably linked to nucleic acid polymers that code for any peptide selected from the group consisting of: immunoglobin-heavy chain, maltose binding protein, glutathione S transferase, Green Fluorescent protein, and ubiquitin. In another variation, the last nucleic acid of the second set of special amino acids, that is, the last special nucleic acid, is operably linked to nucleic acid polymers that code for any peptide comprising any amino acids from 1 to 10,000 amino acids. In still another variation, the last special nucleic acid is operably linked to nucleic acid polymers that code for any peptide selected from the group consisting of: any reporter proteins or proteins which facilitate purification. For example, the last special nucleic acid is operably linked to nucleic acid polymers that code for any peptide selected from the group consisting of: immunoglobin-heavy chain, maltose binding protein, glutathione S transferase, Green Fluorescent protein, and ubiquitin.
In a related aspect, the invention provides any isolated or purified nucleic acid polynucleotide that codes for a protease capable of cleaving the beta secretase cleavage site of APP that contains two or more sets of special nucleic acids, where the special nucleic acids are separated by nucleic acids that code for about 100 to 300 amino acid positions, where the amino acids in those positions may be any amino acids, where the first set of special nucleic acids consists of the nucleic acids that code for DTG, where the first nucleic acid of the first special set of nucleic acids is the first special nucleic acid, and where the second set of nucleic acids code for either DSG or DTG, where the last nucleic acid of the second set of special nucleic acids is the last special nucleic acid, where the first special nucleic acid is operably linked to nucleic acids that code for any number of amino acids from zero to 81 amino acids and where each of those codons may code for any amino acid. In a preferred embodiment, the first special nucleic acid is operably linked to nucleic acids that code for any number of from 64 to 77 amino acids where each codon may code for any amino acid. In a particular embodiment, the first special nucleic acid is operably linked to nucleic acids that code for 71 amino acids. For example, the first special nucleic acid is operably linked to 71 amino acids and where the first of those 71 amino acids is the amino acid T. In a preferred embodiment, the polynucleotide comprises a sequence that is at least 95% identical to a human Asp1 or Asp2 sequence as taught herein. In another preferred embodiment, the first special nucleic acid is operably linked to nucleic acids that code for any number of from 30 to 54 amino acids, or 35 to 47 amino acids, or 40 to 54 amino acids where each codon may code for any amino acid. In a particular embodiment, the first special nucleic acid is operably linked to nucleic acids that code for 47 amino acids. For example, the first special nucleic acid is operably linked to 47 codons where the first those 47 amino acids is the amino acid E.
In another related aspect, the invention provides for any isolated or purified nucleic acid polynucleotide that codes for a protease capable of cleaving the beta (xcex2) secretase cleavage site of APP and that contains two or more sets of special nucleic acids, where the special nucleic acids are separated by nucleic acids that code for about 100 to 300 amino acid positions, where the amino acids in those positions may be any amino acids, where the first set of special nucleic acids consists of the nucleic acids that code for the peptide DTG, where the first nucleic acid of the first special set of amino acids is, the first special nucleic acid, and where the second set of special nucleic acids code for either the peptide DSG or DTG, where the last nucleic acid of the second set of special nucleic acids, the last special nucleic acid, is operably linked to nucleic acids that code for any number of codons from 50 to 170 codons. In a preferred embodiment, the last special nucleic acid is operably linked to nucleic acids comprising from 100 to 170 codons. In a highly preferred embodiment, the last special nucleic acid is operably linked to nucleic acids comprising from 142 to 163 codons. In a particular embodiment, the last special nucleic acid is operably linked to nucleic acids comprising about 142 codons, or about 163 codons, or about 170 codons. In a highly preferred embodiment, the polynucleotide comprises a sequence that is at least 95% identical to aspartyl-protease encoding sequences taught herein. In one variation, the second set of special nucleic acids code for the peptide DSG. In another variation, the first set of nucleic acid polynucleotide is operably linked to a peptide purification tag. For example, the nucleic acid polynucleotide is operably linked to a peptide purification tag which is six histidine. In still another variation, the first set of special nucleic acids are on one polynucleotide and the second set of special nucleic acids are on a second polynucleotide, where both first and second polynucleotides have at lease 50 codons. In one embodiment of this type, both of the polynucleotides are in the same solution. In a related aspect, the invention provides a vector which contains a polynucleotide as described above, or a cell or cell line which is transformed or transfected with a polynucleotide as described above or with a vector containing such a polynucleotide.
In still another aspect, the invention provides an isolated or purified peptide or protein comprising an amino acid polymer that is a protease capable of cleaving the beta (xcex2) secretase cleavage site of APP that contains two or more sets of special amino acids, where the special amino acids are separated by about 100 to 300 amino acid positions, where each amino acid position can be any amino acid, where the first set of special amino acids consists of the peptide DTG, where the first amino acid of the first special set of amino acids is, the first special amino acid, where the second set of amino acids is selected from the peptide comprising either DSG or DTG, where the last amino acid of the second set of special amino acids is the last special amino acid, with the proviso that the proteases disclosed in SEQ ID NO. 2 and SEQ ID NO. 4 are not included. In preferred embodiments, the two sets of amino acids are separated by about 125 to 222 amino acid positions or about 150 to 196 amino acids, or about 150-190 amino acids, or about 150 to 172 amino acids, where in each position it may be any amino acid. In a particular embodiment, the two sets of amino acids are separated by about 172 amino acids. For example, the protease has the amino acid sequence described in SEQ ID NO 6. In another particular embodiment, the two sets of amino acids are separated by about 196 amino acids. For example, the two sets of amino acids are separated by the same amino acid sequences that separate the same set of special amino acids in SEQ ID NO 4. In another particular embodiment, the two sets of nucleotides are separated by about 190 amino acids. For example, the two sets of nucleotides are separated by the same amino acid sequences that separate the same set of special amino acids in SEQ ID NO 2. In one embodiment, the first amino acid of the first special set of amino acids, that is, the first special amino acid, is operably linked to any peptide comprising from 1 to 10,000 amino acids. In another embodiment, the first special amino acid is operably linked to any peptide selected from the group consisting of: any reporter proteins or proteins which facilitate purification. In particular embodiments, the first special amino acid is operably linked to any peptide selected from the group consisting of: immunoglobin-heavy chain, maltose binding protein, glutathione S transferase, Green Fluorescent protein, and ubiquitin. In still another variation, the last amino acid of the second set of special amino acids, that is, the last special amino acid, is operably linked to any peptide comprising any amino acids from 1 to 10,000 amino acids. By way of nonlimiting example, the last special amino acid is operably linked any peptide selected from the group consisting of any reporter proteins or proteins which facilitate purification. In particular embodiments, the last special amino acid is operably linked to any peptide selected from the group consisting of: immunoglobin-heavy chain, maltose binding protein, glutathione S transferase, Green Fluorescent protein, and ubiquitin.
In a related aspect, the invention provides any isolated or purified peptide or protein comprising an amino acid polypeptide that codes for a protease capable of cleaving the beta secretase cleavage site of APP that contains two or more sets of special amino acids, where the special amino acids are separated by about 100 to 300 amino acid positions, where each amino acid in each position can be any amino acid, where the first set of special amino acids consists of the amino acids DTG, where the first amino acid of the first special set of amino acids is, the first special amino acid, D, and where the second set of amino acids is either DSG or DTG, where the last amino acid of the second set of special amino acids is the last special amino acid, G, where the first special amino acid is operably linked to amino acids that code for any number of amino acids from zero to 81 amino acid positions where in each position it may be any amino acid. In a preferred embodiment, the first special amino acid is operably linked to a peptide from about 30-77 or about 64 to 77 amino acids positions where each amino acid position may be any amino acid. In a particular embodiment, the first special amino acid is operably linked to a peptide 35, 47, 71, or 77 amino acids. In a very particular embodiment, the first special amino acid is operably linked to 71 amino acids and the first of those 71 amino acids is the amino acid T. For example, the polypeptide comprises a sequence that is at least 95% identical to an aspartyl protease sequence as described herein. In another embodiment, the first special amino acid is operably linked to any number of from 40 to 54 amino acids (positions) where each amino acid position may be any amino acid. In a particular embodiment, the first special amino acid is operably linked to amino acids that code for a peptide of 47 amino acids. In a very particular embodiment, the first special amino acid is operably linked to a 47 amino acid peptide where the first those 47 amino acids is the amino acid E. In another particular embodiment, the first special amino acid is operably linked to the same corresponding peptides from SEQ ID NO. 3 that are 35, 47, 71, or 77 peptides in length, beginning counting with the amino acids on the first special sequence, DTG, towards the N-terminal of SEQ ID NO. 3. In another particular embodiment, the polypeptide comprises a sequence that is at least 95% identical to the same corresponding amino acids in SEQ ID NO. 4, that is, identical to that portion of the sequences in SEQ ID NO. 4, including all the sequences from both the first and or the second special nucleic acids, toward thexe2x80x94terminal, through and including 71, 47, 35 amino acids before the first special amino acids. For example, the complete polypeptide comprises the peptide of 71 amino acids, where the first of the amino acid is T and the second is Q.
In still another related aspect, the invention provides any isolated or purified amino acid polypeptide that is a protease capable of cleaving the beta (xcex2) secretase cleavage site of APP that contains two or more sets of special amino acids, where the special amino acids are separated by about 100 to 300 amino acid positions, where each amino acid in each position can be any amino acid, where the first set of special amino acids consists of the amino acids that code for DTG, where the first amino acid of the first special set of amino acids is, the first special amino acid, D, and where the second set of amino acids are either DSG or DTG, where the last amino acid of the second set of special amino acids is the last special amino acid, G, which is operably linked to any number of amino acids from 50 to 170 amino acids, which may be any amino acids. In preferred embodiments, the last special amino acid is operably linked to a peptide of about 100 to 170 amino acids or about 142-163 amino acids. In particular embodiments, the last special amino acid is operably linked to a peptide of about 142 amino acids, or about 163 amino acids, or about 170 amino acids. For example, the polypeptide comprises a sequence that is at least 95% identical (and preferably 100% identical) to an aspartyl protease sequence as described herein. In one particular embodiment, the second set of special amino acids is comprised of the peptide with the amino acid sequence DSG. Optionally, the amino acid polypeptide is operably linked to a peptide purification tag, such as purification tag which is six histidine. In one variation, the first set of special amino acids are on one polypeptide and the second set of special amino acids are on a second polypeptide, where both first and second polypeptide have at lease 50 amino acids, which may be any amino acids. In one embodiment of this type, both of the polypeptides are in the same vessel. The invention further includes a process of making any of the polynucleotides, vectors, or cells described herein; and a process of making any of the polypeptides described herein.
In yet another related aspect, the invention provides a purified polynucleotide comprising a nucleotide sequence that encodes a polypeptide having aspartyl protease activity, wherein the polypeptide has an amino acid sequence characterized by: (a) a first tripeptide sequence DTG; (b) a second tripeptide sequence selected from the group consisting of DSG and DTG; and (c) about 100 to 300 amino acids separating the first and second tripeptide sequences, wherein the polypeptide cleaves the beta secretase cleavage site of amyloid protein precursor. In one embodiment, the polypeptide comprises an amino acid sequence depicted in SEQ ID NO: 2 or 4, whereas in another embodiment, the polypeptide comprises an amino acid sequence other than the amino acid sequences set forth in SEQ ID NOs: 2 and 4. Similarly, the invention provides a purified polynucleotide comprising a nucleotide sequence that encodes a polypeptide that cleaves the beta secretase cleavage site of amyloid protein precursor; wherein the polynucleotide includes a strand that hybridizes to one or more of SEQ ID NOs: 3, 5, and 7 under the following hybridization conditions: hybridization overnight at 42xc2x0 C. for 2.5 hours in 6xc3x97SSC/0.1% SDS, followed by washing in 1.0xc3x97SSC at 65xc2x0 C., 0.1% SDS. In one embodiment, the polypeptide comprises an amino acid sequence depicted in SEQ ID NO: 2 or 4, whereas in another embodiment, the polypeptide comprises an amino acid sequence other than the amino acid sequences set forth in SEQ ID NOs: 2 and 4. Likewise, the invention provides a purified polypeptide having aspartyl protease activity, wherein the polypeptide is encoded by polynucleotides as described in the preceding sentences. The invention also provides a vector or host cell comprising such polynucleotides, and a method of making the polypeptides using the vectors or host cells to recombinantly express the polypeptide.
In yet another aspect, the invention provides an isolated nucleic acid molecule comprising a polynucleotide, said polynucleotide encoding a Hu-Asp polypeptide and having a nucleotide sequence at least 95% identical to a sequence selected from the group consisting of:
(a) a nucleotide sequence encoding a Hu-Asp polypeptide selected from the group consisting of Hu-Asp1, Hu-Asp2(a), and Hu-Asp2(b), wherein said Hu-Asp1, Hu-Asp2(a) and Hu-Asp2(b) polypeptides have the complete amino acid sequence of SEQ ID NO. 2, SEQ ID NO. 4, and SEQ ID NO. 6, respectively; and
(b) a nucleotide sequence complementary to the nucleotide sequence of (a).
Several species are particularly contemplated. For example, the invention provides a nucleic acid molecule wherein said Hu-Asp polypeptide is Hu-Asp1, and said polynucleotide molecule of (a) comprises the nucleotide sequence of SEQ ID NO. 1; and a nucleic acid molecule wherein said Hu-Asp polypeptide is Hu-Asp2(a), and said polynucleotide molecule of (a) comprises the nucleotide sequence of SEQ ID NO. 3; and a nucleic acid molecule wherein said Hu-Asp polypeptide is Hu-Asp2(b), and said polynucleotide molecule of (a) comprises the nucleotide sequence of SEQ ID NO. 5. In addition to the foregoing, the invention provides an isolated nucleic acid molecule comprising a polynucleotide which hybridizes under stringent conditions to a polynucleotide having the nucleotide sequence in (a) or (b) as described above. provides an isolated nucleic acid molecule comprising polynucleotide which hybridizes under stringent conditions to a polynucleotide having the nucleotide sequence in (a) or (b) as described above.
Additionally, the invention provides a vector comprising a nucleic acid molecule as described in the preceding paragraph. In a preferred embodiment, the nucleic acid molecule is operably linked to a promoter for the expression of a Hu-Asp polypeptide. Individual vectors which encode Hu-Asp1, and Hu-Asp2(a), and Hu-Asp2(b) are all contemplated. Likewise, the invention contemplates a host cell comprising any of the foregoing vectors, as well as a method of obtaining a Hu-Asp polypeptide comprising culturing such a host cell and isolating the Hu-Asp polypeptide. Host cells of the invention include bacterial cells, such as E. coli, and eukaryotic cells. Among the eukaryotic cells that are contemplated are insect cells, such as sf9 or High 5 cells; and mammalian cells, such as human, rodent, lagomorph, and primate. Preferred human cells include HEK293, and IMR-32 cells. Other preferred mammalian cells include COS-7, CHO-K1, Neuro-2A, and 3T3 cells. Also among the eukaryotic cells that are contemplated are a yeast cell and an avian cell.
In a related aspect, the invention provides an isolated Hu-Asp1 polypeptide comprising an amino acid sequence at least 95% identical to a sequence comprising the amino acid sequence of SEQ ID NO. 2. The invention also provides an isolated Hu-Asp2(a) polypeptide comprising an amino acid sequence at least 95% identical to a sequence comprising the amino acid sequence of SEQ ID NO. 4. The invention also provides an isolated Hu-Asp2(a) polypeptide comprising an amino acid sequence at least 95% identical to a sequence comprising the amino acid sequence of SEQ ID NO. 8.
In still another aspect, the invention provides an isolated antibody that binds specifically to any Hu-Asp polypeptide described herein, especially the polypeptide described in the preceding paragraphs.
The invention also provides several assays involving aspartyl protease enzymes of the invention. For example, the invention provides
a method to identify a cell that can be used to screen for inhibitors of xcex2 secretase activity comprising:
(a) identifying a cell that expresses a protease capable of cleaving APP at the xcex2 secretase site, comprising:
i) collect the cells or the supernatant from the cells to be identified
ii) measure the production of a critical peptide, where the critical peptide is selected from the group consisting of either the APP C-terminal peptide or soluble APP,
iii) select the cells which produce the critical peptide.
In one variation, the cells are collected and the critical peptide is the APP C-terminal peptide created as a result of the xcex2 secretase cleavage. In another variation, the supernatant is collected and the critical peptide is soluble APP, where the soluble APP has a C-terminus created by xcex2 secretase cleavage. In preferred embodiments, the cells contain any of the nucleic acids or polypeptides described above and the cells are shown to cleave the xcex2 secretase site of any peptide having the following peptide structure, P2, P1, P1xe2x80x2, P2xe2x80x2 (SEQ ID NO: 72), where P2 is K or N, where P1 is M or L, where P1xe2x80x2 is D, where P2xe2x80x2 is A. In one embodiment P2 is K and P1 is M and in another embodiment P2 is N and P1 is L.
In still another aspect, the invention provides novel isoforms of amyloid protein precursor (APP) where the last two carboxy terminus amino acids of that isoform are both lysine residues. In this context, the term xe2x80x9cisoformxe2x80x9d is defined as any APP polypeptide, including APP variants (including mutations), and APP fragments that exists in humans, such as those described in U.S. Pat. No. 5,766,846, col 7, lines 45-67, incorporated into this document by reference, modified as described herein by the inclusion of two C-terminal lysine residues. For example, the invention provides a polypeptide comprising the isoform known as APP695, modified to include two lysine residues as its last two carboxy terminus amino acids. An exemplary polypeptide comprises the amino acid sequence set forth in SEQ ID NO. 16. The invention further includes APP isoform variants as set forth in SEQ ID NOs. 18 and 20. The invention further includes all polynucleotides that encode an APP protein that has been modified to include two C-terminal lysines; as well has any eukaryotic cell line comprising such nucleic acids or polypeptides. Preferred cell lines include a mammalian cell line (e.g., HEK293, Neuro2a).
Thus, in one embodiment, the invention provides a polypeptide comprising the amino acid sequence of a mammalian amyloid protein precursor (APP) or fragment thereof containing an APP cleavage site recognizable by a mammalian xcex2-secretase, and further comprising two lysine residues at the carboxyl terminus of the amino acid sequence of the mammalian APP or APP fragment. As taught herein in detail, the addition of two additional lysine residues to APP sequences has been found to greatly increase Axcex2 processing of the APP in APP processing assays. Thus, the di-lysine modified APP reagents of the invention are particularly useful in assays to identify modulators of Axcex2 production, for use in designing therapeutics for the treatment or prevention of Alzheimer""s disease. In one embodiment, the polypeptide comprises the complete amino acid sequence of a mammalian amyloid protein precursor (APP), and further comprises the two lysine residues at the carboxyl terminus of the amino acid sequence of the mammalian amyloid protein precursor. In an alternative embodiment, the polypeptide comprises only a fragment of the APP, the fragment containing at least that portion of APP that is cleaved by a mammalian xcex2-secretase in the formation of Axcex2 peptides.
The practice of assays that monitor cleavage of APP can be facilitated by attaching a marker to a portion of the APP. Measurement of retained or liberated marker can be used to quantitate the amount of APP cleavage that occurs in the assay, e.g., in the presence or absence of a putative modulator of cleavage activity. Thus, in one preferred embodiment, the polypeptide of the invention further includes a marker. For example, the marker comprises a reporter protein amino acid sequence attached to the APP amino acid sequence. Exemplary reporter proteins include a fluorescing protein (e.g., green fluorescing proteins, luciferase) or an enzyme that is used to cleave a substrate to produce a colorimetric cleavage product. Also contemplated are tag sequences which are commonly used as epitopes for quantitative immunoassays.
In a preferred embodiment, the di-lysine-modified APP of the invention is a human APP. For example, human APP isoforms such as APP695, APP751, and APP770, modified to include the two lysines, are contemplated. In a preferred embodiment, the APP isoform comprises at least one variation selected from the group consisting of a Swedish KMxe2x86x92NL mutation and a London V717xe2x86x92F mutation, or any other mutation that has been observed in a subpopulation that is particularly prone to development of Alzheimer""s disease. These mutations are recognized as mutations that influence APP processing into Axcex2. In a highly preferred embodiment, the APP protein or fragment thereof comprises the APP-Sw xcex2-secretase peptide sequence NLDA, (SEQ ID NO: 66) which is associated with increased levels of Axcex2 processing and therefore is particularly useful in assays relating to Alzheimer""s research. More particularly, the APP protein or fragment thereof preferably comprises the APP-Sw xcex2-secretase peptide sequence SEVNLDAEFR (SEQ ID NO: 63).
In one preferred embodiment, the APP protein or fragment thereof further includes an APP transmembrane domain carboxy-terminal to the APP-Sw xcex2-secretase peptide sequence. Polypeptides that include the TM domain are particularly useful in cell-based APP processing assays. In contrast, embodiments lacking the TM domain are useful in cell-free assays of APP processing.
In addition to working with APP from humans and various animal models, researchers in the field of Alzheimer""s also have construct chimeric APP polypeptides which include stretches of amino acids from APP of one species (e.g., humans) fused to streches of APP from one or more other species (e.g., rodent). Thus, in another embodiment of the polypeptide of the invention, the APP protein or fragment thereof comprises a chimeric APP, the chimeric APP including partial APP amino acid sequences from at least two species. A chimeric APP that includes amino acid sequence of a human APP and a rodent APP is particularly contemplated.
In a related aspect, the invention provides a polynucleotide comprising a nucleotide sequence that encodes a polypeptide as described in the preceding paragraphs. Such a polynucleotide is useful for recominant expression of the polypeptide of the invention for use in APP processing assays. In addition, the polynucleotide is useful for transforming into cells to produce recombinant cells that express the polypeptide of the invention, which cells are useful in cell-based assays to identify modulators of APP processing. Thus, in addition to polynucleotides, the invention provides a vector comprising such polynucleotides, especially expression vectors where the polynucleotide is operably linked to a promoter to promote expression of the polypeptide encoded by the polynucleotide in a host cell. The invention further provides a host cell transformed or transfected with a polynucleotide according to claim 14 or a vector according to claim 15 or 16. Among the preferred host cells are mammalian cells, especially human cells.
In another, related embodiment, the invention provides a polypeptide useful for assaying for modulators of xcex2-secretase activity, said polypeptide comprising an amino acid sequence of the formula NH2-X-Y-Z-KK-COOH; wherein X, Y, and Z each comprise an amino acid sequence of at least one amino acid; wherein-NH2-X comprises an amino-terminal amino acid sequence having at least one amino acid residue; wherein Y comprises an amino acid sequence of a xcex2-secretase recognition site of a mammalian amyloid protein precursor (APP); and wherein Z-KK-COOH comprises a carboxy-terminal amino acid sequence ending in two lysine (K) residues. In one preferred variation, the carboxyl-terminal amino acid sequence Z includes a hyrdrophobic domain that is a transmembrane domain in host cells that express the polypeptide. Host cells that express such a polypeptide are particularly useful in assays described herein for identifying modulators of APP processing. In another preferred variation, the amino-terminal amino acid sequence X includes an amino acid sequence of a reporter or marker protein, as described above. In still another preferred variation, the xcex2-secretase recognition site Y comprises the human APP-Sw xcex2-secretase peptide sequence NLDA. It will be apparent that these preferred variations are not mutually exclusive of each otherxe2x80x94they may be combined in a single polypeptide. The invention further provides a polynucleotide comprising a nucleotide sequence that encodes such polypeptides, vectors which comprise such polynucleotides, and host cells which comprises such vectors, polynucleotides, and/or polypeptides.
In yet another aspect, the invention provides a method for identifying inhibitors of an enzyme that cleaves the beta secretase cleavable site of APP comprising:
a) culturing cells in a culture medium under conditions in which the enzyme causes processing of APP and release of amyloid beta-peptide into the medium and causes the accumulation of CTF99 fragments of APP in cell lysates,
b) exposing the cultured cells to a test compound; and specifically determining whether the test compound inhibits the function of the enzyme by measuring the amount of amyloid beta-peptide released into the medium and/or the amount of CTF99 fragments of APP in cell lysates;
c) identifying test compounds diminishing the amount of soluble amyloid beta peptide present in the culture medium and diminution of CTF99 fragments of APP in cell lysates as Asp2 inhibitors. In preferred embodiments, the cultured cells are a human, rodent or insect cell line. It is also preferred that the human or rodent cell line exhibits xcex2 secretase activity in which processing of APP occurs with release of amyloid beta-peptide into the culture medium and accumulation of CTF99 in cell lysates. Among the contemplated test compounds are antisense oligomers directed against the enzyme that exhibits xcex2 secretase activity, which oligomers reduce release of soluble amyloid beta-peptide into the culture medium and accumulation of CTF99 in cell lysates.
In yet another aspect, the invention provides a method for the identification of an agent that decreases the activity of a Hu-Asp polypeptide selected from the group consisting of Hu-Asp1, Hu-Asp2(a), and Hu-Asp2(b), the method comprising:
a) determining the activity of said Hu-Asp polypeptide in the presence of a test agent and in the absence of a test agent; and
b) comparing the activity of said Hu-Asp polypeptide determined in the presence of said test agent to the activity of said Hu-Asp polypeptide determined in the absence of said test agent; whereby a lower level of activity in the presence of said test agent than in the absence of said test agent indicates that said test agent has decreased the activity of said Hu-Asp polypeptide.
In a related aspect, the invention provides a method for assaying for modulators of xcex2-secretase activity, comprising the steps of:
(a) contacting a first composition with a second composition both in the presence and in the absence of a putative modulator compound, wherein the first composition comprises a mammalian xcex2-secretase polypeptide or biologically active fragment thereof, and wherein the second composition comprises a substrate polypeptide having an amino acid sequence comprising a xcex2-secretase cleavage site; (b) measuring cleavage of the substrate polypeptide in the presence and in the absence of the putative modulator compound; and (c) identifying modulators of xcex2-secretase activity from a difference in cleavage in the presence versus in the absence of the putative modulator compound. A modulator that is a xcex2-secretase antagonist (inhibitor) reduces such cleavage, whereas a modulator that is a xcex2-secretase agonist increases such cleavage. Since such assays are relevant to development of Alzheimer""s disease therapeutics for humans, it will be readily apparent that, in one preferred embodiment, the first composition comprises a purified human Asp2 polypeptide. In one variation, the first composition comprises a soluble fragment of a human Asp2 polypeptide that retains Asp2 xcex2-secretase activity. Several such fragments (including xcex94TM fragments) are described herein in detail. Thus, in a particular embodiment, the soluble fragment is a fragment lacking an Asp2 transmembrane domain.
The xcex2-secretase cleavage site in APP is known, and it will be appreciated that the assays of the invention can be performed with either intact APP or fragments or analogs of APP that retain the xcex2-secretase recognition and cleavage site. Thus, in one variation, the substrate polypeptide of the second composition comprises the amino acid sequence SEVNLDAEFR, (SEQ ID NO: 63) which includes the xcex2-secretase recognition site of human APP that contains the xe2x80x9cSwissxe2x80x9d mutation. In another variation, the substrate polypeptide of the second composition comprises the amino acid sequence EVKMDAEF (SEQ ID NO: 67). In another variation, the second composition comprises a polypeptide having an amino acid sequence of a human amyloid precursor protein (APP). For example, the human amyloid precursor protein is selected from the group consisting of APP695, APP751, and APP770. Preferably, the human amyloid precursor protein (irrespective of isoform selected) includes at least on mutation selected from a KMxe2x86x92NL Swiss mutation and a Vxe2x86x92F London mutation. As explained elsewhere, one preferred embodiment involves a variation wherein the polypeptide having an amino acid sequence of a human APP further comprises an amino acid sequence comprising a marker sequence attached amino-terminal to the amino acid sequence of the human amyloid precursor protein. Preferably, the polypeptide having an amino acid sequence of a human APP further comprises two lysine residues attached to the carboxyl terminus of the amino acid sequence of the human APP. The assays can be performed in a cell free setting, using cell-free enzyme and cell-free substrate, or can be performed in a cell-based assay wherein the second composition comprises a eukaryotic cell that expresses amyloid precursor protein (APP) or a fragment thereof containing a xcex2-secretase cleavage site. Preferably, the APP expressed by the host cell is an APP variant that includes two carboxyl-terminal lysine residues. It will also be appreciated that the xcex2-secretase enzyme can be an enzyme that is expressed on the surface of the same cells.
The present invention provides isolated nucleic acid molecules comprising a polynucleotide that codes for a polypeptide selected from the group consisting of human aspartyl proteases. In particular, human aspartyl protease 1 (Hu-Asp1) and two alternative splice variants of human aspartyl protease-2 (Hu-Asp2), a xe2x80x9clongxe2x80x9d (L) form designated herein as Hu-Asp2(a) and a xe2x80x9cshortxe2x80x9d (S) form designated Hu-Asp2(b). As used herein, all references to xe2x80x9cHu-Aspxe2x80x9d should be understood to refer to all of Hu-Asp1, Hu-Asp2(a), and Hu-Asp2(b). In addition, as used herein, all references to xe2x80x9cHu-Asp2xe2x80x9d should be understood to refer to both Hu-Asp2(a) and Hu-Asp2(b). Hu-Asp1 is expressed most abundantly in pancreas and prostate tissues, while Hu-Asp2(a) and Hu-Asp2(b) are expressed most abundantly in pancreas and brain tissues. The invention also provides isolated Hu-Asp1, Hu-Asp2(a), and Hu-Asp2(b) polypeptides, as well as fragments thereof which exhibit aspartyl protease activity.
In a preferred embodiment, the nucleic acid molecules comprise a polynucleotide having a nucleotide sequence selected from the group consisting of residues 1-1554 of SEQ ID NO. 1, encoding Hu-Asp1, residues 1-1503 of SEQ ID NO. 3, encoding Hu-Asp2(a), and residues 1-1428 of SEQ ID NO.5, encoding Hu-Asp2(b). In another aspect, the invention provides an isolated nucleic acid molecule comprising a polynucleotide which hybridizes under stringent conditions to a polynucleotide encoding Hu-Asp1, Hu-Asp2(a), Hu-Asp-2(b), or fragments thereof. European patent application EP 0 848 062 discloses a polypeptide referred to as xe2x80x9cAsp 1,xe2x80x9d that bears substantial homology to Hu-Asp1, while international application WO 98/22597 discloses a polypeptide referred to as xe2x80x9cAsp 2,xe2x80x9d that bears substantial homology to Hu-Asp2(a).
The present invention also provides vectors comprising the isolated nucleic acid molecules of the invention, host cells into which such vectors have been introduced, and recombinant methods of obtaining a Hu-Asp1, Hu-Asp2(a), or Hu-Asp2(b) polypeptide comprising culturing the above-described host cell and isolating the relevant polypeptide.
In another aspect, the invention provides isolated Hu-Asp1, Hu-Asp2(a), and Hu-Asp2(b) polypeptides, as well as fragments thereof. In a preferred embodiment, the Hu-Asp1, Hu-Asp2(a), and Hu-Asp2(b) polypeptides have the amino acid sequence given in SEQ ID NO. 2, SEQ ID NO. 4, or SEQ ID NO.6, respectively. The present invention also describes active forms of Hu-Asp2, methods for preparing such active forms, methods for preparing soluble forms, methods for measuring Hu-Asp2 activity, and substrates for Hu-Asp2 cleavage. The invention also describes antisense oligomers targeting the Hu-Asp1, Hu-Asp2(a) and Hu-Asp2(b) mRNA transcripts and the use of such antisense reagents to decrease such mRNA and consequently the production of the corresponding polypeptide. Isolated antibodies, both polyclonal and monoclonal, that binds specifically to any of the Hu-Asp1, Hu-Asp2(a), and Hu-Asp2(b) polypeptides of the invention are also provided.
The invention also provides a method for the identification of an agent that modulates the activity of any of Hu-Asp-1, Hu-Asp2(a), and Hu-Asp2(b). The inventions describes methods to test such agents in cell-free assays to which Hu-Asp2 polypeptide is added, as well as methods to test such agents in human or other mammalian cells in which Hu-Asp2 is present.
Additional features and variations of the invention will be apparent to those skilled in the art from the entirety of this application, including the drawing and detailed description, and all such features are intended as aspects of the invention. Likewise, features of the invention described herein can be re-combined into additional embodiments that are also intended as aspects of the invention, irrespective of whether the combination of features is specifically mentioned above as an aspect or embodiment of the invention. Also, only such limitations which are described herein as critical to the invention should be viewed as such; variations of the invention lacking limitations which have not been described herein as critical are intended as aspects of the invention.
In addition to the foregoing, the invention includes, as an additional aspect, all embodiments of the invention narrower in scope in any way than the variations specifically mentioned above. Although the applicant(s) invented the full scope of the claims appended hereto, the claims appended hereto are not intended to encompass within their scope the prior art work of others. Therefore, in the event that statutory prior art within the scope of a claim is brought to the attention of the applicants by a Patent Office or other entity or individual, the applicant(s) reserve the right to exercise amendment rights under applicable patent laws to redefine the subject matter of such a claim to specifically exclude such statutory prior art or obvious variations of statutory prior art from the scope of such a claim. Variations of the invention defined by such amended claims also are intended as aspects of the invention.
Sequence ID No. 1: Human Asp-1, nucleotide sequence.
Sequence ID No. 2: Human Asp-1, predicted amino acid sequence.
Sequence ID No. 3: Human Asp-2(a), nucleotide sequence.
Sequence ID No. 4: Human Asp-2(a), predicted amino acid sequence. The Asp2(a) amino acid sequence includes a putative signal peptide comprising residues 1 to 21; and a putative pre-propeptide after the signal peptide that extends through residue 45 (as assessed by processing observed of recombinant Asp2(a) in CHO cells), and a putative propeptide that may extend to at least about residue 57, based on the observation of an observe GRR↓GS (SEQ ID NO: 68) sequence which has characteristics of a protease recognition sequence. The Asp2(a) further includes a transmembrane domain comprising residues 455-477, a cytoplasmic domain comprising residues 478-501, and a putative alpha-helical spacer region, comprising residues 420-454, believed to be unnecessary for proteolytic activity, between the protease catalytic domain and the transmembrane domain.
Sequence ID No. 5: Human Asp-2(b), nucleotide sequence.
Sequence ID No. 6: Human Asp-2(b), predicted amino acid sequence. The Asp2(b) amino acid sequence includes a putative signal peptide, pre-propeptide, and propeptide as described above for Asp2(a). The Asp2(b) further includes a transmembrane domain comprising residues 430-452, a cytoplasmic domain comprising residues 453-476, and a putative alpha-helical spacer region, comprising residues 395-429, believed to be unnecessary for proteolytic activity, between the protease catalytic domain and the transmembrane domain.
Sequence ID No. 7: Murine Asp-2(a), nucleotide sequence.
Sequence ID No. 8: Murine Asp-2(a), predicted amino acid sequence. The proteolytic processing of murine Asp2(a) is believed to be analogous to the processing described above for human Asp2(a). In addition, a variant lacking amino acid residues 190-214 of SEQ ID NO: 8 is specifically contemplated as a murine Asp2(b) polypeptide.
Sequence ID No. 9: Human APP695, nucleotide sequence.
Sequence ID No. 10: Human APP695, predicted amino acid sequence.
Sequence ID No. 11: Human APP695-Sw, nucleotide sequence.
Sequence ID No. 12: Human APP695-Sw, predicted amino acid sequence. In the APP695 isoform, the Sw mutation is characterized by a KMxe2x86x92NL alteration at positions 595-596 (compared to normal APP695).
Sequence ID No. 13: Human APP695-VF, nucleotide sequence.
Sequence ID No. 14: Human APP695-VF, predicted amino acid sequence. In the APP 695 isoform, the VF mutation is characterized by a Vxe2x86x92F alteration at position 642 (compared to normal APP 695).
Sequence ID No. 15: Human APP695-KK, nucleotide sequence.
Sequence ID No. 16: Human APP695-KK, predicted amino acid sequence. (APP695 with two carboxy-terminal lysine residues.)
Sequence ID No.17: Human APP695-Sw-KK, nucleotide sequence.
Sequence ID No. 18: Human APP695-Sw-KK, predicted amino acid sequence
Sequence ID No. 19: Human APP695-VF-KK, nucleotide sequence
Sequence ID No.20: Human APP695-VF-KK, predicted amino acid sequence
Sequence ID No.21: T7-Human-pro-Asp-2(a)xcex94TM, nucleotide sequence
Sequence ID No.22: T7-Human-pro-Asp-2(a)xcex94TM, amino acid sequence
Sequence ID No.23: T7-Caspase-Human-pro-Asp-2(a)xcex94TM, nucleotide sequence
Sequence ID No.24: T7-Caspase-Human-pro-Asp-2(a)xcex94TM, amino acid sequence
Sequence ID No.25: Human-pro-Asp-2(a)xcex94TM (low GC), nucleotide sequence
Sequence ID No.26: Human-pro-Asp-2(a)xcex94TM, (low GC), amino acid sequence
Sequence ID No.27: T7-Caspase-Caspase 8 cleavage-Human-pro-Asp-2(a)xcex94TM, nucleotide sequence
Sequence ID No.28: T7-Caspase-Caspase 8 cleavage-Human-pro-Asp-2(a)xcex94TM, amino acid sequence
Sequence ID No.29: Human Asp-2(a)xcex94TM, nucleotide sequence
Sequence ID No.30: Human Asp-2(a)xcex94TM, amino acid sequence
Sequence ID No.31: Human Asp-2(a)xcex94TM(His)6, nucleotide sequence
Sequence ID No. 32: Human Asp-2(a)xcex94TM(His)6, amino acid sequence
Sequence ID Nos. 33-49 are short synthetic peptide and oligonucleotide sequences that are described below in the Detailed Description of the Invention.
Sequence ID No. 50: Human Asp2(b)xcex94TM polynucleotide sequence.
Sequence ID No. 51: Human Asp2(b)xcex94TM polypeptide sequence (exemplary variant of Human Asp2(b) lacking transmembrane and intracellular domains of Hu-Asp2(b) set forth in SEQ ID NO: 6.
Sequence ID No. 52: Human Asp2(b)xcex94TM(His)6 polynucleotide sequence.
Sequence ID No. 53: Human Asp2(b)xcex94TM(His)6 polypeptide sequence (Human Asp2(b)xcex94TM with six histidine tag attached to C-terminus).
Sequence ID No. 54: Human APP770-encoding polynucleotide sequence.
Sequence ID No. 55: Human APP770 polypeptide sequence. To introduce the KMxe2x86x92NL Swedish mutation, residues KM at positions 670-71 are changed to NL. To introduce the Vxe2x86x92F London mutation, the V residue at position 717 is changed to F.
Sequence ID No. 56: Human APP751 encoding polynucleotide sequence.
Sequence ID No. 57: Human APP751 polypeptide sequence (Human APP751 isoform).
Sequence ID No. 58: Human APP770-KK encoding polynucleotide sequence.
Sequence ID No. 59: Human APP770-KK polypeptide sequence. (Human APP770 isoform to which two C-terminal lysines have been added).
Sequence ID No. 60: Human APP751-KK encoding polynucleotide sequence.
Sequence ID No. 61: Human APP751-KK polypeptide sequence (Human APP751 isoform to which two C-terminal lysines have been added).
Sequence ID No. 62-65: Various short peptide sequences described in detail in detailed description.